The present invention relates to a semiconductor device manufacturing method used for forming an interconnection pattern in a multilevel interconnection structure.
An LSI (Large Scale Integrated circuit) is manufactured by repeating the steps of forming thin films made of various types of materials on a semiconductor substrate and partially removing the thin films by lithography and etching. The role of lithography is to form a pattern having a predetermined size at a predetermined position. The role of etching is to partially remove the thin films from the surface by using the pattern, formed by lithography, as a mask, thereby forming an interconnection made of a thin-film material to have a desired size.
An explanation will be made by way of formation of a gate electrode interconnection of a MOS (Metal Oxide Semiconductor) transistor constituting an LSI.
As shown in FIG. 2A, a gate insulating film 202 is formed on a silicon substrate 201, and a conductive film 203, e.g., polysilicon, is formed on the gate insulating film 202. As shown in FIG. 2B, an anti-reflecting coating (ARC) 204 is formed on the conductive film 203.
As shown in FIG. 2C, a resist pattern 205 is formed on the anti-reflecting coating 204 by known photolithography. In this photolithography, since the anti-reflecting coating 204 is formed under the resist pattern 205, the standing-wave effect which hinders high-precision pattern formation can be prevented.
As shown in FIG. 2D, the anti-reflecting coating 204 is etched by using the resist pattern 205 as a mask, thereby forming a pattern 204a. This etching is performed by dry etching using a gas mixture obtained by adding chlorine (Cl.sub.2) gas or hydrogen bromide (HBr) gas to oxygen gas.
Since the anti-reflecting coating 204 is an organic film, it can be etched by dry etching using oxygen gas. If only oxygen gas is used, side etching occurs to degrade the size precision. Generally, in the reaction process of dry etching, the reaction product can be dissociated in the plasma, can attach to the surface of the processing material again, can be deposited on the surface of the processing material in the plasma, or can cause polymerization reaction on the surface of the processing material. When the organic film is subjected to dry etching by the oxygen gas plasma, the obtained reaction product is mainly CO.sub.2 and H.sub.2 O, which do not cause reattaching and deposition easily.
In contrast to this, for example, if oxygen gas and chlorine gas added to it are used to perform dry etching, deposition caused by plasma polymerization or the like occurs on the surface of the processing material. When deposition occurs on the side surface of the resist pattern 205 or the side surface of the pattern 204a of the anti-reflecting coating 204 that has begun to be exposed by etching, side etching can be suppressed. More specifically, in dry etching of the anti-reflecting coating 204 as the organic film, when an etching gas obtained by adding, e.g., chlorine gas, to the oxygen gas is used, the size precision can be increased.
As shown in FIG. 2E, by using the resist pattern 205 and pattern 204a as the mask, the conductive film 203 is etched to form gate electrodes 203a.
With the conventional method, in the step in FIG. 2D of forming the pattern 204a, since the conductive film 203 is partially overetched at the interface between the pattern 204a and conductive film 203, comparatively large subtrenches 301 are formed, as shown in FIG. 3A. While these subtrenches 301 are present, when the conductive film 203 is etched to form the gate electrodes 203a, the conductive film 203 is etched to disappear faster at the subtrench regions than at other regions because the conductive film 203 at portions corresponding to the subtrenches 301 has a smaller thickness than at other regions.
Thus, when the conductive film 203 at portions other than the gate electrodes 203a is to be completely removed, portions under the subtrenches 301 are also largely overetched. Accordingly, the gate insulating film 202 and part of the silicon substrate 201 are etched to form substrate damages 302, as shown in FIG. 3B.
These defects can be suppressed by decreasing the content of chlorine gas in etching of the anti-reflecting coating 204. More specifically, when the amount of reactive gas, e.g., chlorine gas, decreases, the size of the subtrenches 301 decreases.
When, however, the content of chlorine gas decreases, side etching is started to occur in turn, to cause a decrease in size precision. This causes a defect to lead to a decrease in yield.